The present invention concerns electric contactors, intended to be joined to an electric circuit for warning of braking and to be mounted in sealed engagement in an opening in a rear wall of a pneumatic servomotor casing divided into a front chamber and a rear chamber intercommunicating selectively by a piston means capable of being displaced from a rest position close to the rear wall, the contactor being of the type incorporating a body made of plastic with a first body portion intended to be engaged in the opening in the rear wall of the servomotor casing and a second body portion situated outside the servomotor casing and enclosing at least one pair of electric contacts made of metal capable of being actuated by a follower which is mounted so as to slide in a bore in the first body portion and pushed by a spring towards the outside of this first body portion so as to bear normally against the piston means when the latter is in the region of its rest position.
An electric contactor for warning of braking of this type is described in the document FR-A-No. 2,476,577. In the document, the second body portion of the contactor, coaxial with the first mounting body portion, defines a cavity in which two connecting lugs terminate forming electric contacts which are capable of being joined selectively to one another electrically by a washer carried by the follower of the contactor, the washer/plunger assembly being pushed by a spring bearing, firstly on the bottom of the cavity, and secondly, on the washer. In such an arrangement, the dead travel of closure of the contacts is determined by the position of the piston means of the servomotor relative to the rear wall of its casing. However, in pneumatic servomotors for assisting with braking of the type being considered, the manufacture and assembly tolerances can cause large variations in the positioning of the piston means relative to the rear wall of the casing, which thus results in a large axial dimension of the cavity of the second body portion together with variable conditions of operation as regards establishing the closure of the electric contacts for the spring pushing the follower outwards and establishing the contact pressure of the washer upon the electric contacts.